Keith Strong: Stirling and Hot Air Engines

At CAN we are truly proud of our workforce and love hearing about the achievements that they have outside of the workplace. One of our Principal Engineers, Keith Strong, has a passion for Stirling Engines and has co-written a book all about them! The book was published in 2005 and has become one of the most accessible and leading worldwide sellers in the subject area. You can find a copy of his book here: ‘Stirling and Hot Air Engines: Designing and Building Experimental Model Stirling Engines’  ISBN 186126688X.

Keith’s knowledge and experience is truly impressive, therefore, we asked him to share his insight and give a presentation to CAN employees. Keith’s presentation started with an introduction of the history behind the Stirling cycle and the early machines that the Scottish Dr Rev Robert Stirling patented in 1816. It was interesting to note that the patent didn’t initially recognise the Stirling cycle and the patent office crossed out Stirling and put Steam in its place. It only took 100 years to get that changed. Keith then introduced his varied and extensive background in engineering ranging from Space and Subsea, to Automotive and Viking ships.

In his presentation, Keith examined what an internal combustion engine is, namely Petrol, Diesel, 2 stroke, Jet, Gas turbine, Rocket and Radial and that Stirling engines are classed as external combustion engines along with Steam, and by proxy some electric vehicles when the electricity is generated from burning fuel.

He then moved on to look at non-combustion energy, harvesting in the form of Thermal Electric, Peltier, Solar panels and Solar Stirling showing a 2GW solar Stirling facility. Keith then explained that some applications of Stirling engines have powered submarines, which help significantly in improving their stealth capabilities.

Keith explained that the Stirling cycle can be used not just as a means of producing shaft power as a prime mover, but can also be driven by a motor and act as a heat pump, which led onto his explanation of the Cryocooler variants of the Stirling cycle. He spoke about the pressure temperature exchanges followed by the Carnot cycle. In this section, we got a glimpse of some of the space applications and possibilities of the Stirling cycle machines.

Keith then showed us a liquid piston version of the Stirling engine called a Fluidyne engine which was a remarkably simple, practical and cheap use of the cycle.

Of the 25 variants we were shown, the primary ones included Alpha, Gamma, Beta, Low Temperature differential, Fluidyne, Thermo Acoustic and solar Stirling.

Nuclear applications around the Stirling cycle typically were power generators, where the heat from a nuclear fuel provided the heat source and the Stirling engine side harvested that heat energy and turned it into electricity, perfect for space missions where there is likely to be no solar activity. Examples of these missions are ‘beyond the solar system and deep space’, missions to planets and moons where the ‘sun doesn’t shine’ such as the largest moon of Saturn, Titan. The talk finished with a précis of Stirling applications and advantages that could be used in conjunction with nuclear applications and highlighted remote non photovoltaic solar energy harvesting (Space, Remote, Subsea and Subterranean) which turns out to be more efficient than photovoltaics.

Stirling nuclear applications possible included:

• Self-starting temperature control with non-human interface, automated heat energy transfer.
• Cryogenic levels of cooling, minimal moving parts possible.
• Reliable and long-lasting high-energy transfers.
• An alternative non single point of failure or as a backup generation capacity.
• Works at almost all temperature ranges, Hot & Cold, Hot & Hotter or Cold & Colder.
• Reversible and generative heat control can heat or cool or extract energy from many systems.
• Allows collecting of energy from low grade heat sources.
• Robust and simple, reliable in harsh environments.
• Does not need computers or electronics to function.

It was great to see how many people attended Keith’s presentation; he received some really positive feedback, our employees appreciated discovering something new and interesting that a lot of them hadn’t heard much about. If we ask nicely, we may be treated to further talks on wave propulsion, wing in ground effect hovercraft, designing in space and even Viking ship design!

Thank you to Keith for sharing his knowledge with us all and hosting an insightful presentation and learning session.